Probably the best known contrivance for deodorizing the excreta is the dry earth system as applied in the earth closet, in which advantage is taken of the deodorizing properties of earth. Dry earth is a good deodorizer; 11/2 lb. of dry earth of good garden ground or clay will deodorize such excretion. A larger quantity is required of sand or gravel. If the earth after use is dried, it can be applied again, and it is stated that the deodorizing powers of earth are not destroyed until it has been used ten or twelve times. This system requires close attention, or the dry earth closet will get out of order; as compared with water closets, it is cheaper in first construction, and is not liable to injury by frost; and it has this advantage over any form of cesspit--that it necessitates the daily removal of refuse. The cost of the dry earth system per 1,000 persons may be assumed as follows: Cost of closet, say, L500; expense of ovens, carts, horses, etc., L250; total capital, L750, at 6 per cent. L37 10_s._ interest. Wages of two men and a boy per week, L1 12_s._; keep of horses, stables, etc., 18_s._; fuel for drying earth, 1_s._ 6_d._ per ton dried daily, L1 10_s._; cost of earth and repairs, etc., 14_s._; weekly expenses, L4 14_s._ Yearly expenses, L247 (equal to 4_s._ 11_d._ per ton per annum); interest, L37 10_s._--total, L284 10_s._, against which should be put the value of the manure. But the value of the manure is simply a question of carriage. If the manure is highly concentrated, like guano, it can stand a high carriage. If the manuring elements are diffused through a large bulk of passive substances, the cost of the carriage of the extra, or non-manuring, elements absorbs all profit. If a town, therefore, by adding deodorants to the contents of pails produces a large quantity of manure, containing much besides the actual manuring elements--such as is generally the case with dry earth--as soon as the districts immediately around have been fully supplied, a point is soon reached at which it is impossible to continue to find purchasers. The dry earth system is applicable to separate houses, or to institutions where much attention can be given to it, but it is inapplicable to large towns from the practical difficulties connected with procuring, carting, and storing the dry earth.